Video tape recording signals which are recorded on a tape usually include, besides the video information, several longitudinal tracks which have the audio portion of the program recorded thereon and, in addition, include control signals on the track itself to ensure proper synchronous operating of the video reproducing apparatus with respect to the recording of the information on the tape. The speed of operation of the tape has to be accurately controlled, and the tape itself must carry data which are available to control its speed and, if desired, additionally the speed of a rotating scanner head carrying magnetic tape transducer heads. Many types of video tape recording systems use inclined tracks to carry the video data. These tracks are read by passing the tape in a spiral path over a scanning cylinder within which the scanner heads rotate. The video tracks, thus, are inclined with respect to the longitudinal direction of the tape. In addition to these inclined video tracks, the tape carries longitudinal tracks. One of the longitudinal tracks carries control signals to control the speed of operation of the tape and of the scanner heads. The control signals recorded on this control track usually are square wave pulses with a low duty cycle, in the form of changes of polarity with a usual change in amplitude of 1:1, up to saturation of the magnetic tape. The frequency of these pulses depends on the type of standard TV system being used, and on the type and quality of the magnetic tape, for example.
It is customary to record on one of the inclined video tracks the information contained in about fifty scanning lines of a video-type of reproducer. Such recording of about fifty lines requires a control signal in form of a square wave pulse of 312.5 Hz. In addition, the control track may carry pulses of one-fourth of vertical frequency to form edit pulses; such edit pulses occur in the PAL system at 12.5 Hz, or at 15 Hz in the NTSC system.
The audio information, which may be in the form of stereo audio, is located in a longitudinal track immediately adjacent the control track. Since the space available for the tracks on the tape is limited, the audio track and the control track are close to each other. Some cross talk between the tracks will result. This cross talk is particularly annoying with respect to the audio tracks since low frequencies cause more cross talk than high frequencies. This phenomenon has been discussed in the literature--see Krones: "Die Theorie des Magnetspeichers" in Winckel: "Technik der Magnetspeicher" ("Theory of Magnetic Storage: Technology of Magnetic Storage"), published by Springer, 1960, page 398.
To effect erasing, and particularly erasing of the data on the control track, it has been customary to provide a separate erase signal generator, generating a frequency, for example of 30 kHz, that is, in the supersonic range, which is applied to a separate erase head, or to utilize a combined record/reproduce transducer head.